This invention claims priority of a German filed patent application 199 49 019.8.
The invention concerns a measuring instrument for measuring patterns on substrates of various thicknesses, the measuring instrument comprising an X-Y carriage in which an opening is defined by a peripheral rim, an illumination optical system, and multiple optical compensation elements.
The invention furthermore concerns a method for measuring patterns on substrates of various thicknesses.
Substrates, also called masks, that are to be measured in transmitted light have different thicknesses. Substrates that can be measured in the measuring instrument must meet the SEMI Standard (SEMI P1-92 (copyright) SEMI 1981, 1999). Examples thereof are quartz masks of type 6025 (6xc3x976 inches and 0.25 inches thick) or type 5009 (5xc3x975 inches and 0.09 inches thick), or the quartz mask with dimensions 230xc3x97230xc3x979 millimeters. The standardized thicknesses used by semiconductor manufacturers are 2.3 mm, 3.2 mm, 6.35 mm, and 9 mm. In order to obtain identical measurement conditions (and thus comparable measurement results) for all substrate thicknesses, the optical path length of the measurement beam through the material of the substrate (quartz) must be identical for all substrate thicknesses. The optical system is therefore designed for quartz glass 9 mm thick. When thinner substrates are measured, compensation elements are inserted into the beam path so that the total optical path length achieved is always the same.
U.S. Pat. No. 5,786,897 discloses a method and an apparatus for determining the coordinates of patterns on the surface of a substrate. The apparatus comprises a carriage, movable in X and Y directions, on which is provided a transparent substrate with the pattern to be measured facing downward. A detector device is mounted above the substrate. Interferometers are provided for the X axis and the Y axis, so that the position of the carriage in the X-Y plane can be determined therewith. In order to allow substrates of different thicknesses to be measured, a compensation means for the optical path must be provided. The compensation means comprises a cross-shaped plate in which, for example, four glass elements are provided. The appropriate glass element for the thickness measurement of the substrate is brought into the beam path by rotating the disk. Rotation of the disk can be accomplished by way of a motor or a drive belt. Because of the location of the motorized drive system, a heat source is located in the vicinity of the measurement point, resulting in a degradation in the reproducibility of the measurement. In addition, a great deal of space is needed to accommodate and to move the turret or slider.
It is the object of the invention to create a measuring instrument for measuring patterns on substrates that furnishes reproducible measurement results and also reduces to the greatest extent possible all heat sources present in the measurement region of the measuring instrument. In addition, the design is intended to be as space-saving as possible.
The object is achieved by a measuring instrument which is characterized in that multiple storage compartments for the optical compensation elements are shaped on the peripheral rim of the opening of the X-Y carriage; and that the optical compensation element needed in each case can be removed by the illumination optical system from the associated storage compartment.
A further object of the invention is to create a method with which multiple optical compensation elements can be brought into the beam path of a measuring instrument without thereby influencing the reproducibility of the measurement.
This object is achieved, according to the present invention, in that the method is characterized by the following steps:
determining the substrate type used for the measurement;
displacing the X-Y carriage in such a way that the illumination optical system is positioned beneath the selected compensation element;
raising the illumination optical system and thereby picking up the compensation element; and
displacing the X-Y carriage into the measurement region of the substrate and positioning the illumination optical system, together with the compensation element, in the measurement position.
Advantageous developments are evident from the features of the dependent claims.
With the configuration of the measuring instrument according to the present invention, it is possible to furnish reproducible measurement results and also to exclude the disruptive influence of the motor system for changing the compensation elements. The compensation elements are stored in storage compartments in the substructure of the X-Y carriage. The displacement region of the X-Y carriage is larger than the measurement region in transmitted light. The measurement region corresponds approximately to the opening that is defined in the X-Y carriage. As a result, it is possible for the X-Y carriage itself to move to the corresponding positions and pick up the compensation elements. To prevent incorrect compensation elements from being loaded and thus possibly resulting in damage to the substrate (if the compensation element that is loaded is too thick) or errors in measurement accuracy (if too thin a compensation element is loaded), the compensation elements are coded. For that purpose, the shapes (geometry) are configured such that only the correct compensation fits in each case into the corresponding location. The movement mechanism of the condenser is used to raise the compensation element. A further advantage is achieved with the method according to the present invention, with which it is possible to bring various optical compensation elements into the beam path of the measuring instrument.